Thermal preference influences depth use but not biomass of predatory fishes in response to lake morphometry

Abstract

4Top predators' responses to environmental conditions are now widely recognized as a key part of 1 5 understanding how changing food web architecture influences ecosystem structure and stability, 1 6 ultimately determining the fate of ecosystems with environmental change. Yet the ways that 1 7 fundamental ecosystem properties like size and complexity impact top predators' behaviour are 1 8 not well understood. We examined how lake morphometry impacts the behaviour of three key 1 9fish top predators-the cold-adapted lake trout, the cool-adapted walleye, and the warm-adapted 2 0 smallmouth bass-which can each strongly shape local food web structure. We used a catch-per-2 1 unit-effort database of these key fish species in nearly 500 boreal lakes of Ontario, Canada to 2 2 evaluate the role of thermal preference in driving behavioural and biomass responses to lake 2 3 morphometry. We found strong evidence that species' thermal preferences influence their 2 4 responses to lake size, proportion of littoral area, and mean depth, but we found limited evidence 2 5 that these species respond to lake shape. However, we did not find strong evidence that lake 2 6 morphology influences these species' biomasses. Our results suggest that some aspects of lake 2 7 morphometry can alter habitat accessibility and productivity in ways that influence the behaviour 2 8 and biomass of these top predator species depending their thermal preferences. Our results have 2 9 strong implications for how the food webs of these lakes expand and contract with lake 3 0 morphometry and other key abiotic factors. We argue that several key abiotic factors likely drive 3 1 top predator behaviour in ways that may shape local food web structure and play in important 3 2 role in determining how ecosystems respond to global environmental change. 3 3 3 4